This invention relates to the repair of gas turbine engine hot section components such as turbine airfoils.
Gas turbine engine components operating in the hot gas path environments of such engines are subjected to temperature extremes, oxidation and hot gas corrosion. Thermal barrier coating systems consisting of metallic bond coatings of, e.g., aluminide, Ni-aluminide or the like, followed by ceramic thermal barrier coatings consisting of yttria-stabilized zirconia or the like, are often applied to the surfaces of these components to protect them from such temperature extremes and degradation due to oxidation and hot gas corrosion. The metallic bond coatings typically have a thickness between about 0.001 inch (0.0025 cm) and about 0.004 inch (0.01 cm) for diffusion coatings and between about 0.003 inch (0.0076 cm) and about 0.007 inch (0.018 cm) for overlay coatings. The ceramic thermal barrier coatings typically have a thickness of from about 0.003 inch (0.0076 cm) to about 0.010 inch (0.0025 cm), typically about 0.005 inch (0.013 cm). Eventual degradation of these coatings in service necessitates their removal and re-application at repair intervals. Such removal and re-application of these coatings is a costly process and further results in reduced mechanical properties of the component due to thinning of component walls upon removal of coating interdiffused with substrate as compared to such properties after the prior original application of metallic bond coatings and ceramic thermal barrier coatings. A further disadvantage of removal and re-application of thermal barrier coating systems is that when re-applying the bond coat it is necessary to be concerned with minimizing the potential for in-service coating growth, because excessive coating growth can render the component non-repairable.